This invention is in the field of air seeders and in particular addresses control of the air flow in the air streams in such seeders.
In an air seeder, agricultural materials such as seed, fertilizer, and chemicals are dispensed from respective holding tanks into an air stream that carries the materials through a distribution network, typically a series of tubes and manifolds, to an array of seeding tools mounted along the width of an implement.
The rate of material being applied can vary greatly depending on the crop requirements. An air seeder may be required to apply as low as four or five lb/acre when seeding canola with no fertilizer, and up to 300 lb/acre or more when seeding wheat at high fertilizer rates. Where an air seeder is seeding 40 acres/hour, the air stream must carry about 3 lb/minute of material at the low rate and about 200 lb/minute at the higher rate. Much more air is required at the higher rate to carry the increased amount of material through the system.
It is preferred to have just enough air to carry the material to the furrow openers and maintain uniform distribution across the implement. Where excess air is present, the agricultural materials are traveling at higher speed than necessary when they exit the tube at the furrow opener. The faster the material is traveling when it exits the tube, the more it tends to bounce out of the furrow. Excess speed also can crack and damage seed. On the other hand, where insufficient air flow is present, the distribution across the implement can vary to an unsatisfactory degree. With insufficient air flow, the material being carried will begin to pulsate, and then material will begin to drop out of the air flow and gather at a spot in the distribution network and cause a blockage. Preferably the air flow is maintained at an appropriate level between insufficient and excessive.
Air seeders commonly have two or more tanks mounted on a cart, each tank carrying a particular agricultural material such as seed, fertilizer, chemical or the like. In a xe2x80x9csingle shootxe2x80x9d system, these materials are all metered into a single air stream and carried through a single distribution network such that a blend containing all the materials is deposited in a single furrow. In a xe2x80x9cdouble shootxe2x80x9d system, two distinct and separate air streams and distribution networks are present. One or more materials are metered into each air stream and carried through a corresponding distribution network to be deposited in two separate furrows. Similarly xe2x80x9ctriple shootxe2x80x9d systems are also available providing three distinct and separate air streams and corresponding distribution networks, and increasing multiple systems are foreseeable.
The distinct air streams are typically provided in various ways. A single fan system includes dampers to divide and control the flow of air from the fan into separate air streams each flowing through a corresponding separate distribution network. This type of system is disclosed in U.S. Pat. Nos. 6,296,425 and 6,192,813 to Memory et al., and in 5,996,516 to Benneweis et al. In such a system the total volume of air is varied by varying the fan speed, and the proportion of the total volume directed to each separate air stream is controlled by the dampers. Where the fan speed is held constant, adjusting a damper to direct more air to one air stream will necessarily reduce the volume and speed of the other air streams. In the disclosed systems, a number of sensors monitor the speed of particles carried in the air stream, and the air flow in each air stream is automatically controlled by damper and fan speed adjustments that are made in response to particle speed variations.
Alternatively, a plurality of fans can each provide a separate air stream to each distribution network. The air flow in each air stream is then individually controlled by adjusting each fan speed, and the problem of cross-variation between air flows in separate streams is avoided. Alternatively again in a triple shoot system, a combination system can be provided where one of two fans provides air flow to one air stream, and the other of the two fans provides air flow to two other separate air streams, controlled by dampers.
In conventional seeding systems where the travel speed is substantially constant and where application rates remain constant, the amount of material per minute carried by each air stream, or the material flow rate, remains substantially constant. In such systems the air flow in each air stream can be conventionally adjusted with either manual or remotely controlled damper and fan speed adjusting mechanisms to an appropriate level, such that the air flow is not excessive and yet blockages are avoided. The required air flow also varies with humidity, temperature, and similar atmospheric conditions, as well as altitude. As well sharp slopes in a field can require a higher air flow than is required on flat fields. The material must be pushed uphill from the tank to certain portions of the implement as it moves through the field. Air flow requirements thus increase and decrease as these conditions vary, however the conventional adjustments have allowed for satisfactory operation in conventional fixed rate seeding operations.
Typically the metering devices are driven by a ground drive mechanism so that the amount of material per minute that is dispensed varies directly with ground speed so that the application rate is constant as speed varies. Typically the normal operating ground speed is the maximum speed that will be encountered and when the implement slows for corners and the like, the dispensing rate is reduced, and the air flow is somewhat excessive until normal operating ground speed is again achieved. Thus a conventional air seeder with a constant air flow set as required to carry the material dispensed at a normal ground speed will not experience blockages, since at times the air flow will be excessive, but at no time will the air flow be insufficient.
In practice it is not uncommon when application rates are increased or other conditions change for blockages to occur. The operator then clears the blocked runs manually and increases the air flow to avoid a recurrence. It is also not uncommon for the operator to maintain the higher air flow rate when conditions change again such that a reduced air flow is warranted. It is human nature to avoid blockages which must be manually cleared, and instead opt for excessive air flow which has no immediate consequences for the operator. Higher than necessary air flows are thus common in conventional air seeders.
Recent trends toward variable rate seeding have made air flow adjustment more problematic. In variable rate seeding, the application rate of each agricultural material can be varied by manual or automatic controls that vary the rate of material being dispensed by the metering devices as the machine travels along the field.
In a typical air seeder, the system is calibrated such that for each revolution of a metering device, typically a fluted roller or auger, a known quantity of the metered agricultural material is dispensed into an air stream for distribution across the width of the air seeder. Densities of agricultural materials vary considerably, and such calibration is necessary in order to determine the actual weight of the particular material that is being dispensed per revolution of the metering device.
In conventional seeding, this rotational speed varies only with the ground speedxe2x80x94the operator adjusts the ground drive mechanism to set the ratio between the rotational speed of the metering device and the rotational speed of the wheel on the ground such that the desired application rate results. For every turn of the ground wheel, the seeder will pass over a known area, and the metering device will rotate the required number of times to dispense the amount of agricultural material that is desired to be applied on that area. The desired application rate is thus applied to the field.
In variable rate seeding, this ratio between the rotational speed of the metering device and the rotational speed of the wheel on the ground, or ground speed, can be varied on the go, thus varying the application rate as the seeder moves along the field. The ratio can be varied by the operator manually in response to visual observations of field position, or can be varied automatically to apply rates in accordance with a programmed field map in response to location inputs from a global positioning system (GPS).
Rather than using conventional ground driven metering devices, some variable rate seeders instead drive the metering devices with a motor controlled by a microprocessor. The ground speed and desired application rate are read by the microprocessor which then computes the requisite rotational speed of the metering device and adjusts the speed of the motor to achieve it. As ground speed and application rate vary, the microprocessor continuously computes and adjusts the rotational speed of the metering device.
Where variable rate seeding is used, the amount of material carried by each air stream varies, often quite significantly. Air flow settings in each air stream are consequently conventionally set at that amount of air flow required to carry the amount of material per minute that is required to supply the maximum application rate that will be encountered in order to avoid blockages. The result is that on the majority of the field where the application rate is somewhat below the maximum rate, the air flow in each air stream will be excessive.
The above system of Memory et al. addresses this problem by monitoring the particle velocity in the air stream and making required adjustments to the air flow in each air stream. The Memory system reads the particle velocity in each run with the stated goal of maintaining the minimum particle velocity necessary to successfully carry the particles through the distribution network.
In the Memory et al. system it appears that an initial air flow rate based on product type and mass flow rate is established that is at least sufficient to carry the material through the distribution network, and the particle velocity in each run is then determined. An average or normalized particle velocity for all runs in a distribution network is determined, and the particle velocity in each run is compared to the average. The air flow is reduced incrementally, and if no run has a significantly lower particle velocity than average, it is reduced again, until one run slows down significantly relative to the average, whereupon the last decrease is reversed to avoid a predicted blockage in that run.
In operation, when particle velocity in one run slows down significantly compared to the average velocity of all the runs in a distribution network, the air flow is increased. Also periodically the air flow is reduced as above until one run slows down, whereupon the last decrease is reversed. Thus the minimum air flow is maintained as the implement moves through the field.
The system of Memory et al. is used in variable rate seeding operations. When the variable rate system sends a call over a communications bus for a change in rate the call is received by the metering system and by the air velocity control system. The velocity control system thus knows that more or less air flow will be required and so an initial adjustment to the air flow proportional to the increase or decrease in material flow rate is made by adjusting the fan speed and damper positions. Once this initial adjustment has been made, the air flow is further adjusted with the particle velocity sensing system.
The system of Memory et al. is complex and costly, since a typical double shoot air seeder will have a significant number of runs, each requiring a velocity sensor and connection to the microprocessor. The system appears to have had little, if any, commercial success to date. Presently this complex system is the only alternative to manually adjusting air flow.
A less costly and more simple solution to maintain appropriate air flow levels in conventional and variable rate seeding operations would be desirable. If a simple economical system was available, a significant improvement in operations could be made, with reduced occurrences of blockage from too little air flow, and seed damage and bounce from too much air flow.
It is an object of the present invention to provide for an air seeder a method and system of adjusting the air flow in an air stream in conventional and variable rate air seeding applications that is simple and economical. It is a further object of the present invention to provide such a method and system wherein the fan speed is adjusted to provide an air flow in the air stream that is appropriate for carrying the per minute rate of material being dispensed as that per minute rate varies, either with ground speed or as a result of a change in the per acre application rate.
It is a further object of the present invention to provide such a method and system wherein fan speeds that provide an appropriate air flow for varying material flow rates through a particular distribution network are empirically determined, and used in a microprocessor to adjust fan speeds as per minute dispensing rates vary. It is a further object of the present invention to provide such a method and system wherein a formula is derived from the tabulated fan speeds that will give the appropriate fan speed as a function of application rate and ground speed.
The present invention provides, in one aspect, a system for maintaining an appropriate air flow in an air stream in an air seeder. The system comprises a fan operative to provide an air flow to an air stream, wherein the air stream passes through a distribution network to carry agricultural materials for distribution across a width of a seeding implement. At least one tank contains a granular agricultural material and a metering device is operatively connected thereto that is operative to dispense agricultural material contained in the tank into the air stream. A rotational speed of the metering device is directly proportional to a ground speed of the air seeder such that a per acre application rate dispensed is substantially constant as the ground speed varies. A microprocessor is operatively connected to the air seeder such that the microprocessor receives signals indicating the rotational speed of the metering device and the ground speed. A fan control is operatively connected to the microprocessor and is operative to adjust a speed of the fan to vary the air flow in the air stream in response to signals from the microprocessor. The system is calibrated such that a known weight of agricultural material is dispensed into the air stream for each revolution of the metering device whereby the rotational speed of the metering device multiplied by the known weight per revolution results in a known per minute rate of agricultural material being dispensed into the air stream. The microprocessor is programmed to derive an appropriate fan speed for the per minute rate of agricultural material being dispensed into the air stream and send a signal to the fan control to adjust the speed of the fan to correspond to the appropriate fan speed.
In a second aspect the invention provides a method of maintaining an appropriate air flow in the air stream in an air seeding application wherein a fan provides an air flow in an air stream to carry agricultural material through a distribution network mounted on an air seeder comprising at least one tank containing a granular agricultural material and a metering device operative to dispense agricultural material contained in the tank into the air stream, wherein a rotational speed of the metering device is directly proportional to a ground speed of the air seeder such that a per acre application rate dispensed is substantially constant as the ground speed varies. The method comprises calibrating the system such that a known weight of agricultural material is dispensed into the air stream for each revolution of the metering device and a per revolution dispensing rate is determined, and then multiplying the per revolution dispensing rate by the rotational speed of the metering device to find a known per minute rate of agricultural material being dispensed into the air stream. An appropriate fan speed is determined for the per minute rate of agricultural material being dispensed into the air stream and the speed of the fan is adjusted to correspond to the appropriate fan speed.
Thus in air seeders of the invention, the fan speed is adjusted to provide an air flow in the air stream that is appropriate for carrying the per minute rate of material being dispensed as that per minute rate varies, either with ground speed or as a result of a change in the per acre application rate. While somewhat improved performance could be provided by simply linearly increasing the fan speed as the per minute rate of material being dispensed increased, it is preferred to determine fan speeds that more closely correspond to the actual fan speeds that are appropriate to carry the per minute rate of material being dispensed.
A preferred way to determine what the fan speed should be is to empirically determine by testing what the appropriate fan speed is for varying per minute rates of material being dispensed.
Each distribution network required for various configurations of the air seeder will have its own air flow requirements. The furrow opener spacing, implement width, and manifold configuration being used affect the determination of the required air flow and requisite fan speed. The air flow in any particular implement is also not as a rule, or necessarily, directly proportional to the fan speed. For example a 40 foot wide implement with 12 inch spacing of the furrow openers could have a distribution network comprising a 4 hole primary manifold and four 10 hole secondary manifolds, or a 5 hole primary manifold and five 8 hole secondary manifolds. The appropriate fan speed to provide an appropriate air flow to carry a given per minute rate of material being dispensed through each distribution network will be somewhat different.
To empirically find the requisite fan speed, each distribution network is set up on a test site with the fan connected. It is determined what range of per minute rates of material being dispensed will be carried through the distribution network, and the system is operated at incrementally changing per minute rates from one end of the range to the opposite end. An appropriate air flow is that air flow that is not excessive yet is sufficient to carry the material through the distribution network without plugging. The distribution network is preferably tilted as it would be in field conditions, and an appropriate air flow is determined.
Choosing the appropriate air flow is not a precision calculation, but rather is based on experience as to the terrain conditions that will be encountered, the character and mix of the agricultural materials that will likely be carried, atmospheric conditions, and so forth. When the appropriate air flow is achieved for an increment of dispensing rate, the fan speed that gives that air flow is noted. The process is repeated for each increment of dispensing rates. The fan will have a maximum speed, and a minimum speed will be selected below which the air flow is insufficient for carrying material through the distribution network.
From the tabulated per acre application rates and corresponding fan speeds, a formula is derived which determines the requisite fan speed as a function of the desired per acre application rate and the ground speed. With a known implement width, multiplying the ground speed by the per acre application rate will give a per minute rate of material being dispensed.
In operation at any given per acre application rate, the microprocessor will be reading the ground speed and applying the formula to adjust the fan speed if required by changes in ground speed.
In a variable rate air seeder, when a change in the per acre application rate is indicated to the microprocessor, either manually by an operator or from a GPS system, the microprocessor will (1) adjust the drive ratio so that the metering device dispenses the new desired per acre application rate, and (2) apply the formula with the new desired per acre application rate and current ground speed to find the new appropriate fan speed, and adjust the speed of the fan accordingly.
While the system and method of the invention are particularly suited to variable rate seeding applications, they are also useful in conventional seeding where per acre application rates are constant over a field. The system automatically varies the fan speed as ground speed varies, and when changing per acre application rates from field to field or from one crop to another the fan speed will be automatically adjusted to provide an appropriate air flow.
Extreme conditions can be addressed by providing a step-up and step-down over-ride control whereby the operator can manually increase or decrease the fan speed and thus the air flow, to a higher or lower proportion of the derived appropriate fan speed. In this way the operator can decrease the airflow when conditions warrant, such as when planting seeds that are very susceptible to damage, or increase the air flow when conditions are causing plugging. The system works the same, varying the fan speed as the ground speed and per acre application rate vary, but at a proportionally higher or lower speed.
Typically the appropriate fan speeds will be selected with a safety margin on the high end of an acceptable range to avoid plugging. Where damage susceptible seeds are planted, the operator might choose to reduce the fan speed by 10% to reduce seed damage. Similarly fan speed might be stepped down when working on flat terrain where the implement is level, and it is not required to move material at one end uphill, or stepped up when the terrain is very steep. Atmospheric conditions can be addressed in this manner as well.
The system is readily adapted to a double shoot air seeder with two fans, each supplying air flow to a separate distribution network, or the common single shoot case where seed and fertilizer are carried in and dispensed from two separate tanks into a single air stream that carries a mix of both through a single distribution network.
The system of the invention is much simpler and less costly than the system disclosed in Memory et al. which takes information in xe2x80x9creal timexe2x80x9d, as it is happening, to control air flow such that the minimum air flow required to carry the material through the distribution network is provided.
The system of the present invention rather provides a more appropriate air flow than is provided in conventional air seeders, but does not attempt to provide the minimum air flow. A considerable improvement is provided over conventional air seeders in that the air flow is maintained at a level that is neither overly high or low, and provides satisfactory performance as the per minute rate of material being dispensed varies with the per acre application rate and ground speed.